Abstract

Optoelectronic modulators and couplers frequently require high‐aspect ratio feature definition in thick (≥10 μm) gold. The common process used involves up plating with a photoresist guide. Theory argues that feature boundaries would be degraded due to both diffractive spreading and scattering of the incident light in the resist. This is not observed and near‐90° sidewalls appear obtainable. This letter demonstrates this effect and proposes an explanation for it.